Electric Motor Problem

Electric motor out of a Saniflow Macerator. When power is applied to this motor it just makes a sort of buzzing / humming noise, if at this point the rotor is given a little flick the motor bursts into life. What is wrong with this motor, what has probably caused this fault to occur, and is it fixable?
Interestingly, the motor is filled with oil, I have never come across this before, presumably it is to help with cooling, transfering the heat from the armature to the casing, are all underwater motors built like this?, of course I have now lost some of this as I thought I was accessing a brush and oil started pouring out!
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The starting behaviour you describe is typical of an induction motor where the starting capacitor has failed. These motors rely on a phase lag between the rotor and stator currents generating a restorative magnetic force that provides the torque. This is always prsent (because of friction/load) when the motor is running. When stationary it is not present and a capacitor is added to introduce a starting phase lag. An easy confirmation, can you flick the motor and start it in either direction? If yes, that would confirm the diagnosis. If no then you have another motor stall problem, possibly physical.
As to mending it, probably not worth it if it's all sealed in one case.
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Bob Mannix
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this
this
between
flick
Thanks for the detailed answer
Could the problem have been caused by the motor being jammed in one posistion (unable to turn) while the power is on ?
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Stuart wrote:

Possibly.
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I guess indirectly, if the capacitor was a bit dodgy anyway, excess heat build up from the motor being stalled may have done for it. Difficult to say but the answer isn't "no" ! Older motors of this type sometimes had externally mounted capacitors you could change or were (for example) driving a grinding wheel, where a quick flick in the right direction meant you could carry on using it (ignoring Health and Safety etc!). Yours doesn't sound like you can avoid replacement unless you strip it down, find the capacitor and change it - a new motor would probably be easier!
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I have further dissembled it, see
http://www.stuartstuart.fsnet.co.uk/misc/saniflow.jpg
is the capacitor the large round white thing ? I have been told I may find a large hole burned in the side of it, however it looks in perfect condition.
I have been told a new capacitor will be about 20 which sounds a lot better than the 300 for a whole new unit!
So to sum up, at present the motor just makes a buzzing noise until it is flicked (helped turn) then it starts up and runs as normal. (the motor will run in which ever way it is spun)
So what do you reckon, buy a new capacitor ??
As to the oil i lost out of the motor casing, I was told just refil it with 3:1 is that correct ?
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Stuartsblog explained on 25/03/2008 :

Yes, bottom right hand corner with the blue printing.

They can fail without any outward sign. 20 from the manufacture, probably translates to around 2 from another source - Note the details of the capacitor from the blue printing and source an identical one from the likes of Farnell/CPC/RS Components. The voltage rating and AC rating is very important - most capacitors are designed for DC use.
There is no guarantee that replacement of the capacitor will fix the problem, but for the cost it is worth a try.
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wrote:

Hi Harry
Thanks for the reply and suggestion, I am really struggling to find a replacement capacitor, too many details and specifications, could you point me in the right direction. I have photographed all the specifications on the capacitor, can you tell me what is and what isnt important
http://www.stuartstuart.fsnet.co.uk/misc/capacitor.jpg
Thanks Stuart
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Seems to be a 14 microfarad (+/- 5%) 500 VAC polyester capacitor.
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wrote:

What's the significance of the three different (400/450/500v) ratings?
CPC have a 15uF 450v one, with wire tails. Near enough!
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Glad my initial diagnosis was probably correct. I would concur entirely with Eager Bob's "near enough" !
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Temperature band (A/B/D in this case)
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Phil wrote:

300v AC. 500V DC.
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And how do you work that out, oh wise one?
MBQ
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Man at B&Q wrote:

No need for 500VAC. Its 500VDC to cope with 415V peak to peak voltage of a 230v AC RMS supply.
Actually its more like 275V AC..
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Phil wrote:

IMO it's almost certainly polypropylene (MKP), not polyester (MKT). Pretty-well all AC-rated caps for motor start/run and power-factor correction are polypropylene these days.
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Stuartsblog submitted this idea :

I concur with what other have said...
14uF and rated 400v AC for temperature band A, with a tolerance of + or - 5%. 13uF or 15uF would be fine.
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Harry Bloomfield wrote:

NO. 400V DC is the rating, or around 250V AC. Most motot start caps are quoted as AC rated..
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wrote:

<http://search.ebay.co.uk/search/search.dll ? from=R40&_trksid=m37&satitle=14uF>
cheers, Pete.
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Try doing a search in this group on saniflow+macerator .....
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